The present invention relates in general to the field of utility meters. More particularly, the present invention relates to automatic equipment and systems used for remote reading of utility meters, such as electric, gas, or water meters, via telephone lines. Even more particularly, the present invention relates to a method and apparatus for detecting off-hook and intrusion conditions on a telephone line.
Utility companies use utility usage meters to determine the utility consumption at a customer site. A periodic reading of the utility meter is necessary to determine the usage and to bill the customer for the amount used. The need to send utility company employees to customer sites to read the meters is costly, time consuming, and subject to considerable error. Thus, automated means of recording and reporting the utility usage at customer sites is rapidly replacing the manually read utility meters.
Many companies provide automatic meter reading equipment which is capable of reading meters on customer premises and transmitting the meter readings automatically to a central office of the utility company. Typical systems use both telephone and radio schemes for transmitting the meter readings to the central office.
In the past, there has been on-site meter reading equipment having modem capability which was capable of receiving telephone calls from a central office through the use of special equipment located at the telephone company, and there have also been on-site meters with modems which were capable of transmitting telephone calls to the central office. In general, these systems incorporate an auto-dial, auto-answer modem in each customer site to receive interrogation signals from the telephone line and to formulate and transmit meter readings via the telephone line to the utility company. Prior art systems record information on utility usage and periodically dial into a central office to report the utility usage for recording and billing purposes. These systems are used for reporting electric, gas, and water usage, and the like.
Some prior art systems connect to a customer""s existing telephone line to communicate with the central office by sending information over the telephone lines. The modem shares the telephone line with the customer""s normal usage, such as incoming and outgoing voice communications. Such sharing requires that the system be able to recognize when the telephone line is in use, and to delay demanding use of the telephone line until it is free. Steps must be taken to prevent the data communications system from interfering with other uses and to prevent other uses from corrupting the transmitted data.
The prior art systems have several fundamental shortcomings. For example, when the modem of the utility meter is communicating online with the central office, the customer cannot use the telephone line for dialing out. This is a serious shortcoming if the need arises to dial an emergency number such as 911. Moreover, prior art systems that detect customer""s usage of a telephone line have active circuitry near the telephone terminals (the TIP and RING terminals) to measure the voltage on a telephone line. This active circuitry requires isolated power. This results in complex and costly systems.
It should also be noted that many prior art systems use dedicated lines and do not share a telephone line with the customer""s normal usage. These systems are complex and costly.
Although the art of meter reading via modems and telephone lines is well developed, there remain some problems inherent in this technology, particularly with respect to detecting consumer usage of the telephone line. Therefore, a need exists for a low cost, less complex method and apparatus to detect customer usage of the telephone, such as off-hook and intrusion conditions, so that the customer""s use of the telephone is not affected.
The present invention is directed to an apparatus for determining the state of a telephone line, comprising: voltage to frequency measurement means for measuring a voltage between a TIP terminal and a RING terminal on the telephone line and converting the voltage to a frequency; and comparator means for comparing the frequency with a first value to determine the state of the telephone line.
In the present invention, the voltage to frequency measurement means comprises a voltage to frequency converter and the comparator means comprises a microcontroller, the microcontroller coupled to the voltage to frequency converter to receive the frequency from the voltage to frequency converter. The voltage to frequency converter comprises a RC relaxation oscillator having a tuning element and an active element. The tuning element is a diode and the active element is a comparator.
Furthermore, in accordance with an aspect of the present invention, a TIP/RING filter coupled between the TIP and RING terminals and the voltage to frequency measurement means; and a voltage isolator coupled between the tuning element and the active element. The voltage isolator comprises two coupling capacitors connected in series with the tuning element.
Another aspect of the present invention is directed to means for connecting a modem to the telephone line when the frequency is not less than the first value. Means for disconnecting the modem from the telephone line when the frequency becomes less than a second value are also provided.
In the present invention, means for preventing a telecommunications device from connecting on the telephone line when the frequency is less than the first value are also provided.
In the present invention, the first value is determined responsive to the voltage between the TIP terminal and the RING terminal.
In a further embodiment within the scope of the present invention, an apparatus is provided for determining an intrusion state of a telephone line having a telecommunications device connected thereon, comprising: voltage to frequency measurement means for measuring a voltage between a TIP terminal and a RING terminal on the telephone line and converting the voltage to a frequency; and comparator means for comparing the frequency with a threshold value to determine the intrusion state of the telephone line. Means for disconnecting the telecommunications device from the telephone line when the frequency is less than the threshold value are also provided.
In a further embodiment within the scope of the present invention, an apparatus is provided for determining the state of a telephone line, comprising: measurement means comprising a tuning diode for measuring a voltage between a TIP terminal and a RING terminal on the telephone line; and comparator means for comparing a value responsive to the voltage with a first value to determine the state of the telephone line.
In a further embodiment within the scope of the present invention, an apparatus is provided for determining the state of a telephone line, comprising: measurement means comprising capacitive isolation for measuring a voltage between a TIP terminal and a RING terminal on the telephone line; and comparator means for comparing a value responsive to the voltage with a first value to determine the state of the telephone line.
Another embodiment within the scope of this invention includes an apparatus for detecting an off-hook condition and an intrusion condition on a telephone line, comprising: a voltage to frequency converter for measuring a voltage on the telephone line and converting the voltage to a frequency; and a microcontroller coupled to the voltage to frequency converter for receiving the frequency and determining whether at least one of an off-hook and intrusion condition exists on the telephone line responsive to the frequency. The voltage is a TIP to RING voltage.
In accordance with one aspect of the present invention, a common mode filter is coupled between the telephone line and the voltage to frequency converter, and a voltage isolator coupled between the tuning diode and the comparator.
In accordance with another aspect of the present invention, means are provided to connect a modem to the telephone line when no off-hook condition is detected. Means are also provided to disconnect the modem from the telephone line when an intrusion condition is detected.
In the present invention, the voltage to frequency converter measures the voltage at a predetermined sampling rate. According to one aspect of the present invention, the predetermined sampling rate is one measurement every {fraction (1/16)} seconds.
In the present invention, the off-hook condition is detected when the frequency drops below a first threshold and the intrusion condition is detected when the frequency drops below a second threshold.
In accordance with one aspect of the present invention, memory is provided to store frequency and voltage data used by the microcontroller in the detection of the off-hook and the intrusion conditions.
In a further embodiment within the scope of the present invention, an apparatus is provided for determining the state of a telephone line having an isolation barrier separating the telephone line into a side near a TIP terminal and a RING terminal, and a side away from the TIP terminal and the RING terminal, comprising: measurement means for measuring a voltage between the TIP terminal and the RING terminal on the telephone line, the measurement means being free of a power supply on the side near the TIP terminal and the RING terminal; and comparator means for comparing a value responsive to the voltage with a first value to determine the state of the telephone line.
Another embodiment within the scope of this invention includes an apparatus for determining the state of a signal-carrying line having an isolation barrier separating the signal-carrying line into a side near a first and a second terminal, and a side away from the first and second terminals, comprising: measurement means for measuring a voltage between the first and second terminals, the measurement means being free of a power supply on the side near the first and second terminals; and comparator means for comparing a value responsive to the voltage with a first value to determine the state of the signal-carrying line.
Another embodiment within the scope of this invention includes a method for detecting the state of a telephone line, comprising the steps of: measuring a voltage between a TIP terminal and a RING terminal on the telephone line; and comparing a value responsive to the voltage with a first value to determine the state of
According to one aspect of the present invention, the value is a frequency and the method further comprises the step of converting the voltage to the frequency using a voltage to frequency converter.
According to another aspect of the present invention, the method further comprises connecting a modem to the telephone line when the frequency is not less than the first value; and disconnecting the modem from the telephone line when the frequency becomes less than a second value.
The voltage is measured at a predetermined sampling rate. According to one aspect of the present invention, the predetermined sampling rate is one measurement every {fraction (1/16)} seconds.
According to other aspects of the present invention, the method further comprises the step of setting the first value responsive to the voltage between the TIP terminal and the RING terminal.
Another embodiment within the scope of this invention includes a method for detecting the state of a telephone line, comprising the steps of: measuring a voltage between a TIP terminal and a RING terminal on the telephone line; comparing a value responsive to the voltage with one of a first threshold value and a second threshold value to determine the state of the telephone line; connecting a telecommunications device to the telephone line when the value is not less than the first threshold value; disconnecting the telecommunications device from the telephone line when the value becomes less than the second threshold value; and determining the first threshold value and the second threshold value based on the state of the telephone line and the voltage between the TIP terminal and the RING terminal.
According to one embodiment of the present invention, the method further comprises the steps of measuring a voltage between a TIP terminal and a RING terminal on the telephone line and converting the voltage to a frequency; and comparing the frequency with a threshold value to determine the intrusion state of the telephone line.
Another embodiment within the scope of this invention includes a method for determining an intrusion state of a telephone line having a telecommunications device connected thereon, comprising the steps of: measuring a voltage between a TIP terminal and a RING terminal on the telephone line and converting the voltage to a frequency; and comparing the frequency with a threshold value to determine the intrusion state of the telephone line.
The foregoing and other aspects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.